Ferroelectric devices such as ferroelectric polymer memory devices may comprise one or more layers of ferroelectric material sandwiched between layers of electrodes. Methods of formation of devices such as ferroelectric polymer memory devices may vary, but one method may comprise depositing a layer of ferroelectric polymer on a first electrode layer, and then depositing and patterning a second electrode layer on a substantial portion of the ferroelectric polymer layer.
The prior art uses subtractive metal integration schemes in order to form polymer memory devices. Subtractive metal integration requires first blanket deposition of a metal layer, followed by photoresist spin/expose/develop, then metal etch, then resist removal, then a wet clean. Patterning of conductive polymer subtractively on top of metal poses a number of disadvantages. First, while photoresist can be spin cast upon, developed upon, and chemically removed by wet or dry process techniques from a blanket metal, the same is not true of a blanket conducting polymer layer. For example, if the conducting polymer is soluble in the solvent that is used to spin cast the photoresist, then, during the photoresist spin process on top of a layer of blanket metal covered by a layer of blanket conducting polymer, the photoresist solution will simply rinse the conducting polymer off. However, even if an appropriate conducting polymer is chosen so as not to be soluble in photoresist solvent, and a layer of photoresist could be spin cast on top of the conductive polymer without damaging it, chemical development of the UV exposed photoresist would destroy the conducting polymer in the areas where the developer dissolved the polymer. This is because of the chemical process used in exposing and developing chemically amplified photoresists. UV light disintegrates acid groups in the photoresist making light-exposed sections dissolvable in a basic solution of TMAH (tetramethylammoniumhydroxide). Once this base solution has rinsed off the UV exposed photoresist regions, the conducting polymer below would be exposed to the base solution. Conducting polymers are acid doped, and therefore the developer TMAH would either de-dope the polymer by neutralizing the doping acids, or simply dissolve the polymer entirely, even undercutting the photoresist that was not developed, thus removing all of the conducting polymer from the substrate. Finally, even assuming that means existed for circumventing the disadvantages set forth above, in the end, there would be patterned conducting polymer only on top of patterned metal, this being insufficient because the patterned metal line sidewalls would be left exposed to the ferroelectric polymer that is subsequently spin cast on the patterned substrate. The ferroelectric polymer and the metal on the sidewalls would chemically react, damaging the ferroelectric polymer.
A need, therefore, exists for an improved method of forming a ferroelectric polymer memory device that addresses at least some of the above concerns.